1. Field of the Invention
The present invention relates to the determination of air density for use in controlling the cooling of electronic systems, such as computers.
2. Description of the Related Art
Cooling fans are commonly used to cool electronic devices, such as computers. For example, on-board cooling fans are installed in individual computer servers, and blower modules are often included within multi-blade chassis or enclosures to cool multiple blade servers housed in the chassis. It is recognized in the design of air cooling systems that air density decreases with increasing altitude, and that lower air density requires greater volumes of air flow to achieve an equivalent level of cooling.
Some cooling fans are operated at a single-speed that is fast enough to achieve the desired air flow and cooling at any altitude. Consequently, these fans run faster than necessary at lower altitudes, resulting in a waste of energy, excessive noise and accelerated wear on the fans. Although this mode of operation is simple, it does not address the demands placed on modern computer systems.
Other systems may include an on-board altimeter within each device. Accordingly, the speed of each device's cooling fan is regulated in relation to an altitude sensed by the altimeter. One problem with such a solution is that many electronic systems, such as rack-based computer systems, have many different components or subsystems, each requiring its own cooling fan. Equipping each component or subsystem with a dedicated on-board altimeter could significantly increase the cost of the electronic system as a whole. System reliability and maintenance might also suffer because each altimeter is subject to potential failure.
Still further, the rising prevalence of notebook computers means that user-input altitude is unworkable. As the notebook computer travels from place to place, the altitude may change routinely. Current altitude information may be particularly important for a notebook computer, since unnecessary high fan speeds will drain the batteries. However, the portability of the notebook computer dictates that any altimeter device must be compact and avoid consumption of significant electrical energy.
Therefore, there is a need for an improved cooling system and method for measuring air density in a computer system. In particular, it would be desirable to have a reliable source of air density or altitude that enables greater accuracy in the control of air flow through a computer system. Accordingly, excessive air flow rates should be avoided while providing sufficient control of computer component temperatures.